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Another Medium for Enumerating Citrate-Fermenting Bacteria in Lactic Cultures

Department of Dairying, University of Tennessee, Knoxville

ABSTRACT

Galesloot et al. (1) developed agar media for isolating and enumerating aroma bacteria in starters. We found their whey agar with casaminoacids and 0.5% calcium lactate (WACCA%) to be adequate but troublesome to prepare. Therefore, we altered the WACCA% by substituting commercial Tomato Juice Agar¹ (TJA) for the whey agar containing casaminoacids. The streptococci inhibitor, calcium lactate, and the aroma bacteria indicator, calcium citrate, were retained as in the original medium. The altered medium contains 15 g TJA and 5 g calcium lactate in water to make one liter.

The altered medium, tomato juice agar, containing 0.5% calcium lactate (TJAC%), was tested against WACCA% by plate-count enumerations of bacteria in known cultures. Three skimmilk cultures were used: A, a 20-hr culture of Streptococcus lactis; B, a four-day culture of citrate-fermenting bacteria from a lactic culture; and C, a mixture of 25 ml each of A and B. Cultures A and B were held in an ice bath for 1 hr before Culture C was made, then all remained in the ice bath until plated.